1. Field of the Invention
The present invention relates to machine recognition of images and, more particularly, to techniques for locating address blocks in digitized images of mail pieces for subsequent processing by optical character recognition (OCR) techniques.
2. Description of the Related Art
Due to the ever increasing volumes of mail being handled by the world's post offices and commercial delivery organizations, automated handling and sorting of mail pieces is increasingly being employed. Automated address recognition using optical character recognition (OCR) techniques is an important part of any such sorting process.
In order to allow efficient address recognition, it is necessary to know where address information is located in an image of an entire mail piece.
Consequently much effort has been directed to the development of so-called Address Block Location (ABL) techniques. This is a difficult image recognition task because there are no tight rules which determine either where an address will be located on an envelope, or the shape or size of the address. Furthermore, a wide variety of extraneous data such as portraits, other text and logos, as well as stamps, labels and postmarks, may also be found on an envelope and confuse the matter. Moreover, in many cases, more than one address, for example sender and receiver addresses, may appear on an envelope.
In addition, problems in image acquisition may give rise to poor image quality. For example, colored backgrounds may cause distortion or loss of information and use of cellophane windows may increase the reflectivity of the address area. Likewise, noise, dirt and poor scanning can produce low image quality.
Examples of various prior art ABL techniques can be found in P. W. Palumbo et al "Postal Address Block Location in Real Time," IEEE Computer, Vol 25, No 9, pp 34-42 (1992), J. C. Oriot et al "Address Block Location on Flat Mail Pieces by a Bottom Up Segmentation," Trait. Signal (France) Vol 12, No 2 (1995) pp 213-223 (1995), and A. L. Basso et al U.S. Pat. No. 5,386,482. A. C Downton et al "Pre-Processing of Envelope Images for Optical Character Recognition," Proc. Ninth International Conference on Pattern Recognition, Nov. 14-17, 1988, pp 27-31, proposes an ABL technique which includes horizontal and vertical smearing of low resolution envelope images followed by a heuristic selection of an address block.
Typically, the prior art as exemplified in the above referenced articles and other papers to which they refer has employed computationally intensive processes such as connected component analysis or OCR in order to identify text areas. These are costly procedures, even for a low-resolution image, and such a heavy computational load has generally led to the use of special purpose hardware for address block location in commercial applications. Furthermore, such algorithms are very sensitive to noise and consequently preprocessing to remove noise from the image is required, which preprocessing can potentially remove useful information from the image.